Fully automated wafer debonding system and method thereof

ABSTRACT

An apparatus and method for debonding a pair of bonded wafers are disclosed herein. In some embodiments, the debonding apparatus, comprises: a wafer chuck having a preset maximum lateral dimension and configured to rotate the pair of bonded wafers attached to a top surface of the wafer chuck, a pair of circular plate separating blades including a first separating blade and a second separating blade arranged diametrically opposite to each other at edges of the pair of bonded wafers, wherein the first and the second separating blades are inserted between a first and a second wafers of the pair of bonded wafers, and at least two pulling heads configured to pull the second wafer upwardly so as to debond the second wafer from the first wafer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 62/968,363, filed on Jan. 31, 2020, which isincorporated by reference herein in its entirety.

BACKGROUND

In order to manufacture integrated circuits, semiconductor wafers areused to form integrated circuits. During the manufacturing process,integrated circuits are fabricated through a plurality of processingsteps (e.g., etching steps, lithography steps, deposition steps, etc.)performed upon a semiconductor wafer (e.g., a silicon wafer), followedby dicing the semiconductor wafer into separate integrated circuits. Insome applications, the wafers are bonded together to form a wafer stack.In other applications, in order to realize higher integration, simplifypackaging processes, or to couple circuits or other components, two ormore wafers may be bonded together before the dicing step, which allowsthe integrated circuits to be fabricated on both sides of the waferafter a thin down. Moreover, since a wafer level bonding shows anincreased promise for “More than Moore” technologies, where added valueis provided to devices by incorporating functionality that does notnecessarily scale according to Moore's Law, wafer debonding is becominga desired process for separating one wafer from another. Furthermore,during the inspection of the bonded wafer, the bonding may be found tobe defective and the wafers may need to be debonded from each other. Ifbonding of the wafer stack is successful, some residual process may beperformed on the wafer to complete the manufacturing process.

However, some wafer stacks are difficult to separate using conventionalmechanical or chemical methods. In addition, wafers are sometimesrelatively thin making them ill-suited to withstand the forces appliedduring debonding processes. As such, wafers may experience failureduring the debonding process. Current single sided wafer debondingsystems and methods use a flat blade that is repeatedly (e.g., fourtimes) inserted and retracted at the bevel region of the wafer while thewafer rotates 360° degrees. However, current wafer debonding systems andmethods are inefficient and often result in wafer breakages and largeedge defect rates at the opposite side of the flat blade insertionpoint. On the other hand, the double sided debonding systems and methodshave a lower risk of defects near the wafer edges, but may require alarger pull force which may result in wafer breakages. Accordingly,current wafer debonding systems and methods are not entirelysatisfactory.

The information disclosed in this Background section is intended only toprovide context for various embodiments of the invention described belowand, therefore, this Background section may include information that isnot necessarily prior art information (i.e., information that is alreadyknown to a person of ordinary skill in the art). Thus, work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the present disclosure are described indetail below with reference to the following Figures. The drawings areprovided for purposes of illustration only and merely depict exemplaryembodiments of the present disclosure to facilitate the reader'sunderstanding of the present disclosure. Therefore, the drawings shouldnot be considered limiting of the breadth, scope, or applicability ofthe present disclosure. It should be noted that for clarity and ease ofillustration these drawings are not necessarily drawn to scale.

FIG. 1A illustrates an example of a wafer debonding system for debondinga pair of bonded wafers using a pair of circular plate blades, inaccordance with some embodiments of the present disclosure.

FIG. 1B illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a plurality of separating bladesequally spaced from each other around the wafers, in accordance withsome embodiments of the present disclosure.

FIG. 1C illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of circular plate bladesrotating in a reverse direction of the rotating wafers, in accordancewith some embodiments.

FIG. 2 illustrates a cross-sectional view of an application of a waferdebonding system for debonding bonded wafers, in accordance with someembodiments of the present disclosure.

FIG. 3A illustrates cross-sectional and top views of a separating bladeof a wafer debonding system shown in FIG. 1A, 1B, 1C, or 2, inaccordance with some embodiments.

FIG. 3B illustrates a top view of a wafer debonding system with de-bondwavefronts, in accordance with some embodiments.

FIG. 4 illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of pulling heads withdifferent pull forces, in accordance with some embodiments.

FIG. 5 illustrates a flow diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of circular plate blades,in accordance with some embodiments.

DETAILED DESCRIPTION

Various exemplary embodiments of the present disclosure are describedbelow with reference to the accompanying figures to enable a person ofordinary skill in the art to make and use the present disclosure. Aswould be apparent to those of ordinary skill in the art, after readingthe present disclosure, various changes or modifications to the examplesdescribed herein can be made without departing from the scope of thepresent disclosure. Thus, the present disclosure is not limited to theexemplary embodiments and applications described and illustrated herein.Additionally, the specific order and/or hierarchy of steps in themethods disclosed herein are merely exemplary approaches. Based upondesign preferences, the specific order or hierarchy of steps of thedisclosed methods or processes can be re-arranged while remaining withinthe scope of the present disclosure. Thus, those of ordinary skill inthe art will understand that the methods and techniques disclosed hereinpresent various steps or acts in a sample order, and the presentdisclosure is not limited to the specific order or hierarchy presentedunless expressly stated otherwise.

FIG. 1A illustrates an exemplary wafer debonding system 100A fordebonding a pair of bonded wafers according to some embodiments. Asshown in FIG. 1A, a wafer chuck 105 is provided for holding a firstwafer 101 a and a second wafer 101 b bonded to each other. In thisexemplary embodiment, the wafer chuck 105 may be attached to a suitablefixture 103 using mechanical, electrical, or magnetic attachmentstechniques. In some further embodiments, the first wafer 101 a may beattached to the wafer chuck 105 using a vacuum suction technique.Moreover, the first 101 a and the second 101 b bonded wafers may beplaced on the wafer chuck 105 with the first wafer 101 a in directcontract with a top surface of the wafer chuck 105. In variousembodiments, the second wafer 101 b may be bonded to the first wafer 101a through direct or indirect bonding techniques. For example, the secondwafer 101 b may be bonded to the first wafer 101 a through siliconfusion bonding, oxide bonding, hybrid bonding, or adhesive bondingtechniques.

Referring to FIG. 1A, the wafer debonding system 100A may include a pairof blades 107 that are placed at edges of the bonded wafers 101 a and101 b. In some embodiments, the pair of blades 107 may be arrangeddiametrically opposite to each other (i.e., on opposite sides of thebonded wafers 101 a and 101 b) or at a preset angle from one anotherwith respect to a center axis of rotation of the bonded wafers 101 a and101 b. In various embodiments, the pair of blades 107 may have a shapeof a circular plate with a diameter 107 a in a range of from about 14 mmto about 50 mm and a thickness 107 b in a range of from about 2 mm toabout 6 mm. In some further embodiments, as shown in an exemplarycross-sectional edge view 111, the pair of blades 107 may havetriangular shaped edges. In other embodiments, the pair of blades 107may have circular or square shaped edges.

The separating blades 107 may be inserted in an area between the firstwafer 101 a and the second wafer 101 a and the area may have a bevelededge to assist with the insertion, in accordance with some embodiments.In various embodiments, pulling heads 113 a and 113 b may respectivelybe attached to coil springs 113 c and 113 d that are configured tocontrol first and second pulling forces 113 f and 113 g. In someembodiments, the pulling heads 113 a and 113 b continuously assert thefirst and second pulling forces 113 f and 113 g as the pair of blades107, arranged diametrically opposite to each other, are rotatablyinserted between the first and second wafers 101 a and 101 b by anincreasing amount until an automatic optical inspection (AOI) system 109detects that the first and second wafers 101 a and 101 b have beende-bonded on at least one edge (and/or on both edges). The insertionpoint may, in some embodiments, be precisely controlled with the AOIsystem 109, which may include, for example, motors, actuators, and otheroptical instruments, as well as a controller circuitry and/or aprocessor for performing the operations described herein. In somefurther embodiments, the AOI system 109, may further include a pair ofthree-dimensional cameras or charge-coupled device cameras configured tocheck the debonding processes and provide information to the controllerand/or processor for further adjustment of the separating blades 101 aand 101 b. In various embodiments, the AOI system 109 may also determinehow much further the blades 101 a and 101 b should be inserted betweenthe first wafer 101 a and the second wafer 101 b, or whether to increaseor decrease the pulling forces 113 f and 113 g applied to the secondwafer 101 b. Moreover, the AOI system 109 may also measure an insertingspeed, depth, and slope of the pair of blades 107 and feedback themeasured parameters to the controller that is configured to control therotating speed of the pair of blades 107 and the rotating speed of thefirst 101 a and second 101 b bonded wafers.

In some further embodiments, a flex wafer assembly may be provided tohold and move the second wafer 101 b of the pair of bonded wafers. Theflex wafer assembly may be controlled by programmable drive motors andmay be configured to receive the measured parameters such as theinserting speed, depth, and slope of the pair of blades 107 from the AOIsystem. In some embodiments, the flex wafer assembly may comprise atleast two pulling heads, the first pulling head 113 a and the secondpulling head 113 b that are placed diametrically opposite to each otherabout a central axis of the wafer chuck (and/or about a central axis ofthe pair of bonded wafers).

The pulling heads 113 a and 113 b may be configured to applylongitudinal pull forces that are perpendicular to the surface of thesecond wafer 101 b and to separate and remove the second wafer 101 bfrom the first wafer 101 a. In various embodiments, the longitudinalpull forces may be in a range of from about 0.1 kilogram-force (kgf) toabout 10 kilogram-force (kgf). The pulling forces in the above disclosedrange can provide a sufficient torque, while minimizing the risk ofwafer breakage. In some embodiments, different pull forces may beapplied by the pulling heads 113 a and 113 b in order to provideunbalanced torques which may result in a more efficient debondingprocess. As such, the amount of the unbalanced torques may be determinedbased on a debonding crack length estimated from the cross-sectionalshape of the pair of blades 107. In some embodiments, the pulling head113 a is configured as a suction cup attached to a coil spring 113 c andto a vacuum hose/conduit 113 e. In some embodiments, the vacuumhose/conduit runs through the coil spring 113 c. The pulling head 113 bmay be constructed in similar fashion as the pulling head 113 a, and isattached to a second coil spring 113 d and second vacuum conduit 113 e.Moreover, each of the vacuum conduits 113 e may be attached to a vacuumsource configured to provide a desired vacuum pressure to the pullinghead 113 a. In some embodiments, the same vacuum source may be shared bythe pulling heads 113 a and 113 b. In some embodiments, the pullingheads 113 a and 113 b may have adjustable top vacuum cup positions, forexample, in a range of from about 3 cm to about 9 cm above the topsurface of the second wafer 101 b. In one embodiment, a vacuum systemmay be shared by the pulling heads 113 a and 113 b providing the pullforces. Moreover, the pulling heads 113 a and 113 b may be powered bymotors or other actuators configured to pull up the second wafer 101 b,after the bonded wafers are rotated by 180° degrees or by one or morecircles. In some embodiments, an angle of rotation of the bonded wafers101 a and 101 b is based on the separation success rates, wafer breakagerates, wafer defects rates, and/or wafer scratch rates.

In various embodiments, a pair of coil springs 113 c and 113 d may beattached to the pulling heads 113 a and 113 b to buffer the pull forcesand to minimize a hard landing on the bonded wafers. In someembodiments, the pair of coil springs may have different springcoefficients, such that a first pull force applied by the first pullinghead 113 a is smaller than a second pull force applied by the secondpulling head 113 b. In this regard, spring coefficients of the pair ofcoil springs can be in a range of from about 1×10² N/m to about 1×10⁵N/m to provide soft landing on the bonded wafers. In some embodiments,to provide sufficiently unbalanced torques on the first and secondpulling heads 113 a and 113 b, the spring coefficient of a first coilspring can be, for example, 10 to 100 times greater than the springcoefficient of the second coil spring.

FIG. 1B illustrates a schematic diagram of a wafer debonding method 100Bfor debonding a pair of bonded wafers using a plurality of separatingblades equally spaced from each other around the bonded wafers, inaccordance with some embodiments. As shown in FIG. 1B, a pair of bondedwafers 101 can be separated using a pair of separating blades 115 a and115 b having different thicknesses and inserted therebetween from edgesof the pair of bonded wafers 101. In various embodiments, the pair ofseparating blades 115 a and 115 b is arranged diametrically opposite toeach other. In some embodiments, a plurality of separating blades may beused for the wafer debonding process 100B. This approach may result in asmaller amount of wafer rotations. For example, separating blades 115 a,119 a, 121 a, 123 a, 115 b, 119 b, 121 b and 123 b may be equally spacedfrom each other and arranged around the bonded wafers 101. Morespecifically, the separating blades 115 a, 119 a, 121 a, 123 a, 115 b,119 b, 121 b and 123 b may be arranged around the bonded wafers 101spaced by 45° degrees from each other. This arrangement of theseparating blades, in particular, allows for only 45° wafer rotation toachieve a debonding crack around the edges of the bonded wafers 101.

FIG. 1C illustrates a schematic diagram of a wafer debonding method 100Cfor debonding a pair of bonded wafers 101 using a pair of circular plateblades 114 a and 114 b that rotate in an opposite direction of the pairof rotating bonded wafers 101, in accordance with some embodiments. Forexample, as shown in FIG. 1C, the bonded wafers 101 can be rotated in aclockwise direction by the wafer chuck, while the circular plate blades114 a and 114 b are rotated in a counter-clockwise direction, inaccordance with some embodiments. In this way, damage to the edge orbevel of the bonded wafers 101 can be significantly reduced. In someembodiments, rotation as well as insertion speeds of the circular plateblades 114 a and 114 b may be different. In some embodiments, therotation and insertion speeds of each of the circular plate blades 114 aand 114 b are individually controlled by the AOC system 109, asdescribed above.

FIG. 2 illustrates a schematic diagram of a single side of a waferdebonding system 200 for debonding a pair of bonded wafers according tosome embodiments. The wafer debonding system 200 comprises of aseparating blade 203 having a thickness 205 and a wafer chuck 202 e thatis concentric to a pair of bonded wafers 201 a and 201 b during thedebonding process. As shown in FIG. 2, the separating blade 203 isinserted between the edges of the pair of bonded wafers 201 a and 202 b.In some embodiments, a pair of separating blades may also be arrangeddiametrically opposite to each other with respect to the bonded wafers201 a and 201 b. In some embodiments, such pair of separating bladeshave the same thickness and are configured to be inserting between theedges of the pair of bonded wafers 201 a and 202 b on opposite sides ofthe bonded wafers 201 a and 201 b.

In some embodiments, a diameter of the wafer chuck 202 e may be in arange of from about 150 mm to about 250 mm such that peripheral edgeportions of the bonded wafers 201 a and 202 b have enough space todeform while receiving sufficient support from the wafer chuck 202 e. Insome embodiment, the diameter of the wafer chuck 202 e may be smallerthan the maximum diameter of the pair of bonded wafers 201 a and 201 b.A free standing length or a induced crack length L 202 needed forperforming the debonding process may be determined based on thefollowing relationship:

${\gamma = {\frac{3}{8}\left( \frac{Et^{3}y^{2}}{L^{4}} \right)}},$

where γ is the surface energy related to the work required to cut a bulksample of a first wafer 201 a, E is the Young's modulus, which ismeasures the stiffness of the bonded wafers 201 a and 201 b, t is thethickness 202 a of the wafer 201 a, 2y is a thickness 203 of aseparating blade 205, and L is the induced crack length 202 formedbetween the bonded wafers. As such, given a range of acceptablethicknesses 203 for the separating blade 205 and a range of acceptablewafer chuck diameters, a range for the induced crack length L 202 may bedetermined based on the above disclosed relationship. For example, ifthe separating blade 205 thickness is in the range of 1×10⁻³ to 2×10⁻⁴meters (m), the surface energy is in the range of 0.2 to 0.5 J/m², andthe wafer chuck's 202 e diameter is in the range of 154.042159 to248.089 mm, than the range for the induced crack length L 202 is in therange of 72.97892052 to 25.95538 mm, given that silicon's Young'smodulus is 1.3×10¹¹ Pa and the thickness of the bonded wafers is0.000775 mm.

FIG. 3A illustrates cross-sectional views of exemplary separating blades301, 302 and 303 that can be used in the wafer debonding systems shownand described with respect to FIGS. 1A, 1B, 1C, and 2 above, inaccordance with various embodiments of the present disclosure. Forexample, a separating blade 301 may have a pointed end as shown in thecross-sectional view illustrated in FIG. 3A. In some embodiments, theseparating blade 301 may have a thickness T₁ in the range of about 2 mmto about 4 mm. In some embodiments, the separating blade may have aleading portion having a depth L₁ in the range of about 2 mm to about 5mm. As shown in FIG. 3A, a separating blade 302 may have a rounded frontwedge as shown in the cross-sectional view designed to reduce scratchrisk. In some embodiments, the separating blade 302 may have a thicknessT₂ in a range of from about 2 mm to about 10 mm and a leading portionhaving depth L₂ in a range of from about 2 mm to about 10 mm. As furthershown in FIG. 3A, a separating blade 303 may have a square front wedgeas shown in the cross-sectional view. In some embodiments, theseparating blade 303 may have a thickness T₃ in a range of about 2 mm toabout 4 mm and leading portion having a depth L₃ in a range of about 3mm to about 5 mm.

In various embodiments, the separating blades shown in FIG. 3A can bemade of a material with a small scratch hardness (e.g., smaller than 5gigapascals (GPa) when the wafers to be debonded are made of silicon) toreduce scratch risk, and a high Young's modulus (e.g., greater thanabout 3 gigapascals (GPa)) to create an initial debonding area withoutwafer defects. In some embodiments, the scratch hardness of theseparating blades 301, 302 and 303 can be smaller than that of thematerial of wafers to be debonded (e.g. wafers 101 a, 101 b in FIG. 1).In other embodiments, the separating blades 301, 302 and 303 can be madeof polyetheretherketone (PEEK), Aluminum (Al), or Teflon with a scratchhardness in a range of from about 0.05 GPa to about 0.3 GPa, and aYoung's modulus in a range of from about 3 GPa to 3.95 GPa, or othermaterials exhibiting such Young's modulus and hardness.

FIG. 3B illustrates a top view of a debonding process performed by awafer debonding system shown in FIG. 1, in accordance to someembodiments. During the debonding process, a separating blade 307 may beinserted into a wafer 305 at a length d 309. Moreover, based on theinitial pull force applied by the pulling heads 113 a and 113 b (FIG.1A), an initial debonding area can expanded to an enlarged debondingarea d′ 311 (as shown by dashed lines) thereby reducing the risk ofwafer cracks.

FIG. 4 illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of pulling heads withdifferent pull forces, in accordance with some embodiments. As shown inFIG. 4, a first separating blade 409 a and a second separating blade 409b are inserted between a first wafer 401 a and a second wafer 401 b to afirst distance d1 and a second distance d2, respectively, during adebonding process. In some embodiments, the first distance d1 may beequal to the second distance d2. The first insertion distance d1 and thesecond insertion distance d2 can respectively be in a range of fromabout 8 mm to about 12 mm optimized to reduce the possibility of waferbreakage. In some embodiments, strain sensors 416 may be utilized tomonitor the mechanical compression of the second wafer 401 b during theinsertion of the first and second blades 409 a and 409 b, in order toavoid wafer breakages. In some embodiment, the strain sensors 416 maygauge the mechanical displacement of the second wafer 401 b bygenerating an electrical signal as a function of the straining pressureimposed during the debonding process. In some embodiments, the strainsensors 416 comprise of a resistive transducer 417 that converts themechanical elongation or compression of the second wafer 401 b into aresistance change. In further embodiments, pressure sensors 418 may becoupled to the first and second blades 409 a and 409 b and configured tomeasure pressure asserted on the bonding interface of the first andsecond wafers 401 a and 401 b. For example, if the first blade 409 a orthe second blade 409 b are inserted into the first wafer 401 a or secondwafer 401 b, instead of in between the bonded wafers, a high pressuremay be detected by the pressure sensors 418. In other embodiments, theAOI system 109 (FIG. 1A) may be used to control the insertion distancesd1 and d2.

Referring still to FIG. 4, the pair of bonded first and second wafers401 a and 401 b may have a preset maximum diameter D 403. In variousembodiments, the preset maximum diameter D 403 may be optimized toreduce the possibility of wafer breakage. As such, in some embodiments,the preset maximum diameter D 403 may be 12 inches (i.e. 300 mm) wafersbefore dicing and packaging. In further embodiments, the bonded wafers401 a and 401 b are placed on a wafer chuck 407 and are concentric tothe wafer chuck 407. In some embodiments, the wafer chuck 407 has apreset maximum lateral dimension (e.g., a diameter if circular) D′ 405that is smaller than the maximum diameter D of the bonded wafers 401 aand 401 b. For example, the maximum dimension D′ 405 of the wafer chuck407 may be 8 inches. In some embodiments, the maximum dimension 405 D′can be about 0.5 to about 0.9 times of the maximum diameter D of thebonded wafers 401 a and 401 b, such that the bonded wafers 401 a and 401b have a desired peripheral space (free-standing peripheral area) forperforming the debonding process. In some embodiments, the maximumdimension 405 D′ may be determined so that the wafer chuck 407 providesa desired back support to the bonded wafers 401 a and 401 b and reducesthe possibility of wafer breakage using the debonding process. In someembodiments, the wafer chuck 407 may have the maximum dimension 405 D′in a range of from about 150 mm (millimeter) to about 250 mm.

In some embodiments, the wafer debonding method may use a pair ofpulling heads 415 a and 415 b arranged diametrically opposite to eachother for pulling up the second wafer 401 b. In some furtherembodiments, more than two pulling heads can also be placed on a topsurface of the second wafer 401 b for lifting off the second wafer 401 bfrom the first wafer 401 a. Moreover, the plurality of the pulling headsmay be arranged according to a certain pattern such as linear, circular,or parabolic, in order to provide enhanced pulling forces. Furthermore,the pulling forces provided by the plurality of the pulling heads may beunbalanced and individually controlled by the AOC system 109, forexample.

Based on the arrangements described above, the two separating blades 409a and 409 b, inserted at different depths between the bonded wafers 401a, 401 b, may cause a fulcrum to move to different positions. Forexample, initial insertion depths d1 and d2 of the two separating blades409 a and 409 b, respectively, may result in fulcrums positioned at aninitial distance d 411 from the pulling heads 415 a, 415 b. Furthermore,as the insertion depths of the two separating blades 409 a and 409 bincreases, the fulcrums may be positioned at a distance d′ 413 from thepulling heads 415 a, 415 b. In some embodiments, a larger insertiondepth may enhance debonding wave propagation and reduce debonding force,and thus, a smaller wafer bending is introduced on each side of the pairof bonded wafers 401 a and 401 b to reduce the possibility of waferbreakage.

FIG. 5 illustrates a flow diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of circular plate blades,in accordance with some embodiments. Although a method 500 is describedin relation to FIGS. 1-4, it will be appreciated that the method 500 isnot limited to such structures disclosed in FIGS. 1-4 and may standalone independent of the structures disclosed in FIGS. 1-4. In addition,some operations of the method 500 may occur in different orders and/orconcurrently with other operations or events apart from thoseillustrated and/or described herein. Moreover, not all illustratedoperations may be required to implement one or more aspects orembodiments of the present disclosure. Further, one or more of theoperations depicted herein may be carried out in one or more separateoperations and/or phases.

At operation 501, a pair of bonded wafers are placed onto a wafer chuck.In some embodiments, the pair of bonded wafers may be attached to thewafer chuck using a vacuum. In various embodiments, prior to operation501, a first wafer of the pair of bonded wafers may be processed to formfeatures, such as circuits, connecting layers, contacts, and otherapplicable structures. In some embodiments, a second wafer of the pairof bonded wafers may include a substrate made of semiconductor,sapphire, thermoplastic polymer, oxide, carbide, or other suitablematerial.

At operation 503, a bonding interface of the first and second wafers islocated using an automatic optical inspection (AOI) system. For example,a pad probe or an optical scan may be performed over the edge surfacesof the bonded wafers. In further embodiments, at operation 503, wafersmisalignment and whether the interface voids are in the desired regionsmay be determined. Furthermore, the AOI system may also determine adistance from a pair of circular plate blades to the pair of bondedwafers.

At operation 505, based on a feedback received from the AOI system, arobotic arm or other mechanism move the blades to a closest point nearthe interface. In some embodiments, the robotic arm comprises a bladeportion configured to support a separating blade and may include sensorsto enhance the positioning of the blade portion with respect to the pairof bonded wafers to prevent scratching a surface of the pair of bondedwafers. In some embodiments, the blade portion is substantially U-shapedto minimize the amount of contact between the blade portion and theedges of the bonded wafers. At operation 507, the pair of blades areslowly inserted into the bonding interface of the first and secondwafers from edges to facilitate the debonding of the first and secondwafers. In some embodiments, pressure detectors may be used to monitor,in real-time, the pressure applied to the first and second wafer duringthe insertion of the pair of blades. In this embodiment, the real-timepressure monitoring reduces the risk of wafer breakages during theoperation 507. In this regard, the pressure measurements received fromthe pressure detectors may also help to determine how much further thepair of blades ought to be inserted between the first wafer and thesecond wafer or whether to retract the inserted pair of blades to avoidwafer breakage. In some embodiments, during the insertion operation 507,the pair of blades may be rotating in an opposite direction of therotating wafer chuck.

At operation 509, the bonded wafers are rotated multiple times throughthe rotating chuck attached to the bottom surface of the first wafer. Insome embodiments, the bonded wafers are rotated four times, by 45°degrees during each rotation. In other embodiments, the bonded wafersmay be rotated by more than 360° degrees depending on the wafersubstrate type and/or other manufacturing process needs.

At operation 511, two pulling heads are attached to the upper surface ofthe second wafer by creating the vacuum inside the pulling heads. Atoperation 513, the first wafer is debonded and separated from the firstwafer. The debonding process can be performed using the debonding systemand methods disclosed in this application. A pair of different or samepull forces can be utilized to facilitate the debonding process whilesimultaneously retracting the pair of inserted blades. This will resultin fewer edge defects and/or reduced wafer breakage rates. At operation515, the debonded first wafer and second wafer are inspected for surfacedefects, brakes and scratches. At operation 517, the debonded surfacesof the first wafer and the second wafer may be reworked by replacing,cleaning, or re-polishing defective wafers.

While various embodiments of the present disclosure have been describedabove, it should be understood that they have been presented by way ofexample only, and not by way of limitation. Likewise, the variousdiagrams may depict an example architectural or configuration, which areprovided to enable persons of ordinary skill in the art to understandexemplary features and functions of the present disclosure. Such personswould understand, however, that the present disclosure is not restrictedto the illustrated example architectures or configurations, but can beimplemented using a variety of alternative architectures andconfigurations. Additionally, as would be understood by persons ofordinary skill in the art, one or more features of one embodiment can becombined with one or more features of another embodiment describedherein. Thus, the breadth and scope of the present disclosure should notbe limited by any of the above-described exemplary embodiments.

It is also understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations are used herein as a convenient means of distinguishingbetween two or more elements or instances of an element. Thus, areference to first and second elements does not mean that only twoelements can be employed, or that the first element must precede thesecond element in some mariner

Additionally, a person having ordinary skill in the art would understandthat information and signals can be represented using any of a varietyof different technologies and techniques. For example, data,instructions, commands, information, signals, bits and symbols, forexample, which may be referenced in the above description can berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

A person of ordinary skill in the art would further appreciate that anyof the various illustrative logical blocks, modules, processors, means,circuits, methods and functions described in connection with the aspectsdisclosed herein can be implemented by electronic hardware (e.g., adigital implementation, an analog implementation, or a combination ofthe two), firmware, various forms of program or design codeincorporating instructions (which can be referred to herein, forconvenience, as “software” or a “software module), or any combination ofthese techniques.

To clearly illustrate this interchangeability of hardware, firmware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware,firmware or software, or a combination of these techniques, depends uponthe particular application and design constraints imposed on the overallsystem. Skilled artisans can implement the described functionality invarious ways for each particular application, but such implementationdecisions do not cause a departure from the scope of the presentdisclosure. In accordance with various embodiments, a processor, device,component, circuit, structure, machine, module, etc. can be configuredto perform one or more of the functions described herein. The term“configured to” or “configured for” as used herein with respect to aspecified operation or function refers to a processor, device,component, circuit, structure, machine, module, signal, etc. that isphysically constructed, programmed, arranged and/or formatted to performthe specified operation or function.

Furthermore, a person of ordinary skill in the art would understand thatvarious illustrative logical blocks, modules, devices, components andcircuits described herein can be implemented within or performed by anintegrated circuit (IC) that can include a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device, orany combination thereof. The logical blocks, modules, and circuits canfurther include antennas and/or transceivers to communicate with variouscomponents within the network or within the device. A processorprogrammed to perform the functions herein will become a speciallyprogrammed, or special-purpose processor, and can be implemented as acombination of computing devices, e.g., a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suitableconfiguration to perform the functions described herein.

If implemented in software, the functions can be stored as one or moreinstructions or code on a computer-readable medium. Thus, the steps of amethod or algorithm disclosed herein can be implemented as softwarestored on a computer-readable medium. Computer-readable media includesboth computer storage media and communication media including any mediumthat can be enabled to transfer a computer program or code from oneplace to another. A storage media can be any available media that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can include RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer.

In this document, the term “module” as used herein, refers to software,firmware, hardware, and any combination of these elements for performingthe associated functions described herein. Additionally, for purpose ofdiscussion, the various modules are described as discrete modules;however, as would be apparent to one of ordinary skill in the art, twoor more modules may be combined to form a single module that performsthe associated functions according embodiments of the presentdisclosure.

Various modifications to the implementations described in thisdisclosure will be readily apparent to those skilled in the art, and thegeneral principles defined herein can be applied to otherimplementations without departing from the scope of this disclosure.Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the novel features and principles disclosed herein, asrecited in the claims below.

What is claimed is:
 1. A debonding system for debonding a pair of bondedwafers, comprising: a wafer chuck having a preset maximum lateraldimension and configured to rotate the pair of bonded wafers attached toa top surface of the wafer chuck; a pair of circular plate separatingblades including a first separating blade and a second separating bladearranged diametrically opposite to each other at edges of the pair ofbonded wafers, wherein the first and the second separating blades areinserted between a first and a second wafers of the pair of bondedwafers; and at least two pulling heads configured to pull the secondwafer upwardly so as to debond the second wafer from the first wafer. 2.The debonding apparatus of claim 1, wherein a cross section of a leadingportion of each of the pair of separating blades has a shape selectedfrom: a rounded wedge, a square wedge and a triangular wedge.
 3. Thedebonding apparatus of claim 1, wherein each of the pair of separatingblades have a Young's modulus in a range of from about 3 Gigapascal(GPa) to about 3.95 Gigapascal (GPa).
 4. The debonding apparatus ofclaim 4, wherein the pair of separating blades are configured to rotatein an opposite direction of the rotating pair of bonded wafers.
 5. Thedebonding apparatus of claim 1, wherein, during an insertion process,the pair of separating blades are controlled by an automatic opticalinspection (AOI) system configured to control insertion depths of thepair of separating blades.
 6. The debonding apparatus of claim 5, theAOI system is further configured to determine insertion points forinserting the pair of separating blades between the bonded wafers. 7.The debonding apparatus of claim 5, further comprising at least onepressure detector configured to monitor pressure applied to the firstand second wafer during the insertion process of the pair of blades. 8.The debonding apparatus of claim 1, wherein the at least two pullingheads are configured to apply at least a first pull force and a secondpull force, respectively.
 9. The debonding apparatus of claim 8, whereinthe first and second pull forces are set to be unequal.
 10. A debondingsystem, comprising: a wafer chuck having a preset maximum lateraldimension and configured to rotate the pair of bonded wafers attached toa top surface of the wafer chuck; a plurality of circular plateseparating blades that are equally spaced from each other and arrangedaround the pair of bonded wafers and configured to rotate in an oppositedirection of the rotating pair of bonded wafers, wherein the pluralityof circular plate separating blades are rotatably inserted between afirst and a second wafers of the pair of bonded wafers; a flex waferassembly comprising of at least two pulling heads configured to pull thesecond wafer upwardly so as to debond the first wafer from the secondwafer; and an automatic optical inspection (AOI) system comprising ofthree-dimensional cameras configured to monitor a debonding process,wherein the AOI system transmits feedback signals to actuatorscontrolling the plurality of circular plate separating blades and the atleast two pulling heads of the flex wafer assembly.
 11. A debondingsystem of claim 10, wherein the plurality of separating blades rotate atdifferent speeds.
 12. A debonding system of claim 10, wherein theplurality of separating blades have a thickness in a range of from about2 mm to about 6 mm.
 13. A debonding system of claim 10, wherein a firstseparating blade from the plurality of separating blades is insertedbetween the bonded wafers to a first distance, and a second separatingblade from the plurality of separating blades is inserted between thebonded wafers to a second distance that is different from the firstdistance.
 14. A debonding system of claim 10, the AOI system is furtherconfigured to measure an inserting speed, depth, and slope of theplurality of separating blades and feedback the measured insertingspeed, depth, and slope to a controller that is configured to controlthe rotating speed of the plurality of separating of blades and therotating speed of the bonded wafers.
 15. A method for debonding a pairof bonded wafers, the method comprising: attaching a pair of bondedwafers onto a wafer chuck using vacuum suction; determining a bondinginterface between the pair of bonded wafer using an automatic opticalinspection (AOI) system; determining a distance from a pair of circularplate blades to the pair of bonded wafers using the AOI system;inserting the pair of circular plate blades the bonding interface usinga robotic arm; rotating the pair of bonded wafers by rotating the waferchuck attached to the bonded wafers; and pulling up a top wafer of thepair of bonded wafers so as to debond the pair of bonded wafers, whilesimultaneously retracting the pair of blades from the bonded wafers. 16.The method of claim 15, further comprising: inspecting surface defectsof the debonded wafers.
 17. The method of claim 16 further comprising:cleaning and re-polishing the debonded surfaces.
 18. The method of claim17 further comprising: rotating the pair of bonded wafers four times,wherein each rotation is by 45 degrees.
 19. The method of claim 1,further comprising: monitoring, using pressure detectors, pressure inthe pair of bonded wafers during the inserting step of the pair ofblades.
 20. The method of claim 15, wherein the pair of blades arerotated in an opposite direction to the rotating wafer chuck.